U.S. Pat. Ser. No. 4,674,834 issued Jun. 23, 1987 discloses an electronic scanner and a printer which employ fiber optic bundles. The bundle has its fibers arranged in a linear array in a first face and in an area array in a second face. In operation as a scanner, light is directed at a paper and the linear end, having a length which can scan an 8.5 inch width of a paper, is moved incrementally with respect to the paper from one linear scan position to the next. Pixels transmitted by the fibers are sensed by a sensor array optically coupled to the area face.
In operation as a printer, an array of light sources is coupled to the area face of the bundle and the linear face is optically coupled to a photosensitive medium such as an electrostatic medium or photosensitive. An array of light sources generates patterns of pixels which are transferred to the photosensitive medium, line-by-line, for later transfer to paper by the familiar xerographic process.
A large number of fibers is necessary in order to achieve commercially acceptable resolution using fiber optic bundles. For example, for three hundred dots per inch resolution, for an eight and one half inch wide document, 2,650 fibers are required; for six hundred dots per inch, over 5,100 are required. It has been found that the manufacture of such fiber optic bundles is costly not only because of fiber breakage, but also because of the initialization procedure necessary to identify the relationships between the fiber ends of the two faces of a (noncoherent) fiber optic bundle as explained in that patent.
Copending patent application Ser. No. 532,932 (now U.S. Pat. No. 5,155,790) filed Jun. 4, 1990 and assigned to the assignee of the present application discloses a fiber optic bundle which has the fiber ends arranged in a linear array in a first face and in an area array in a second face. But the bundle is composed of ribbons of fibers. That is to say, each ribbon is composed of a plurality of fibers arranged in parallel. Each fiber is capable of transmitting multiple pixels. In addition, the application discloses an embodiment in which each fiber in each ribbon is a multicore fiber composed of rows and columns of fibers, each also capable of conducting light, but each of a diameter small compared to the pixel size (the light source image).
The fiber optic bundle is constructed with such ribbons by abutting ribbons in a side-by-side arrangement to form the linear face of the bundle. The area face is formed by stacking the opposite ends of the ribbons one on top of the other. Particularly if care is taken, for example, to arrange the ribbons so that consecutively numbered ribbons, for example, from left to right in the linear face, correspond to the order from bottom to top in the area face, initialization is at least simplified if not obviated because the relationships between fiber ends is ordered.
Also, breakage is reduced because ribbons are stronger and easier to handle. Still, great care is required in the construction of the bundles to ensure that the ribbons align with one another and the spacings between the ribbons are uniform. Otherwise, the bundle does not transmit an image faithfully.
In the operation of a printer which is composed of ribbons of fibers of this type, light is directed from a plurality of light sources to an oscillating mirror which moves the (changing) image of the light sources along an axis perpendicular to the axis of the of the ribbons. Thus, in practice, twenty-four light emitting diodes LED's direct light towards the mirror which reflects the image at consecutive, like-numbered fibers in twenty-four ribbons. Thus, an on-off pattern of light from the LED's is directed at the first fibers of the ribbon, then the second fibers, then the third . . . etc.
As the succession of patterns are thus generated, the photosensitive drum juxtaposed with the linear face of the bundle is moving. Thus, the consecutive pixels within a ribbon are tilted, with respect to the initial intended line of the drum to an extent which is a function of the speed of rotation of the drum, leading to an undesirable misalignment of pixels.